While Microsoft may ponder about the number of users of Hotmail falling, while Gmail increases, one happy user is apparently al-Qaeda operations mastermind Khalid Sheik Mohammed.

It has been revealed that in the days following the September 11 terrorist attacks, alleged intended to use his free Hotmail account to direct a US-based operative to carry out an attack. A guilty plea agreement filed by Al Saleh Kahlah al-Marri in  a US federal court shows that al-Qaeda used technology such as pre-paid calling cards, public phones, computer search engines and simplistic codes to communicate, plan and carry out its operations.

Al-Marri also surfed the Internet to research cyanide gas, using software to cover his tracks, according to the document filed Thursday in federal court in Peoria, Illinois. He marked the locations of dams, waterways and tunnels in the United States in an almanac.

He sent e-mails to Khalid Sheik Mohammed's hotmail account, , addressed to "Muk" and signed "Abdo". The details of that code were found in an address book in Pakistan. Apparently the email address is still live although no one answers it.

Al-Marri tried to use a Yahoo e-mail account to contact Mohammed, but it failed to go through. So he switched to Hotmail because it was more reliable. You can't buy advertising like that.